Modulating electromagnetic radiation, and in particular switching optical signals between two or more intensities or phases is used to encode information on an optical signal for purposes such as communication or storage of information. The amount of information that can be encoded is related to the rate or frequency at which modulation can be performed.
At relatively low modulation rates, optical modulation can be performed by, for example, modulating the current to a laser diode. Modulating the current to turn the laser diode on or off is often referred to as on-off keying (OOK). Such on-off current modulation generates an intensity modulated optical signal.
To achieve intensity modulation at very high modulation rates a common technique is to separate the optical signal into two components, phase modulate at least one component such that a 180 degree relative phase shift can be introduced between the two components which are then recombined. Modulating the phase in this manner results in an intensity modulated optical signal, as in a conventional Mach Zehnder modulator.
Another conventional technique for modulating or switching an optical signal is to use a Pockels cell, which is a voltage controlled wave-plate based on the electro-optic effect. A Pockels cell is typically combined with a polarizer and can switch the plane of polarization of an optical signal between zero optical rotation and 90° rotation at high speeds. Such a rotation enables redirecting the optical signal by means of a polarized beam splitter.
Operation of a Mach Zehnder modulator or a Pockels cell modulator depends on weak bulk material effects of the phase modulating material of the Mach Zehnder modulator and the voltage controlled wave-plate material of the Pockels cell. The requirement of modifying bulk properties of a material to achieve modulation has speed limiting consequences and places a significant burden on the manufacturing and operation of these devices, requiring a Mach Zehnder modulator to be physically long and requiring high voltage for operation of a Pockels cell modulator. These burdens have negative physical size and cost consequences.
There is therefore an unmet need for a method, apparatus and system for high speed a optical modulator or switch that is not limited by speed limitations of bulk material based modulators and is not limited by the physical size and cost issues of bulk material based modulators.